On Mon, 2018-12-31 at 14:09 -0500, Chuck Lever wrote: > > On Dec 31, 2018, at 1:59 PM, Trond Myklebust < > > trondmy@xxxxxxxxxxxxxxx> wrote: > > > > On Mon, 2018-12-31 at 13:44 -0500, Chuck Lever wrote: > > > > On Dec 31, 2018, at 1:09 PM, Trond Myklebust < > > > > trondmy@xxxxxxxxxxxxxxx> wrote: > > > > > > > > On Thu, 2018-12-27 at 17:34 -0500, Chuck Lever wrote: > > > > > > On Dec 27, 2018, at 5:14 PM, Trond Myklebust < > > > > > > trondmy@xxxxxxxxxxxxxxx> wrote: > > > > > > > > > > > > > > > > > > > > > > > > > On Dec 27, 2018, at 20:21, Chuck Lever < > > > > > > > chuck.lever@xxxxxxxxxx> > > > > > > > wrote: > > > > > > > > > > > > > > Hi Trond- > > > > > > > > > > > > > > I've chased down a couple of remaining regressions with > > > > > > > the > > > > > > > v4.20 > > > > > > > NFS client, > > > > > > > and they seem to be rooted in this commit. > > > > > > > > > > > > > > When using sec=krb5, krb5i, or krb5p I found that multi- > > > > > > > threaded > > > > > > > workloads > > > > > > > trigger a lot of server-side disconnects. This is with > > > > > > > TCP > > > > > > > and > > > > > > > RDMA transports. > > > > > > > An instrumented server shows that the client is under- > > > > > > > running > > > > > > > the > > > > > > > GSS sequence > > > > > > > number window. I monitored the order in which GSS > > > > > > > sequence > > > > > > > numbers appear on > > > > > > > the wire, and after this commit, the sequence numbers are > > > > > > > wildly > > > > > > > misordered. > > > > > > > If I revert the hunk in xprt_request_enqueue_transmit, > > > > > > > the > > > > > > > problem goes away. > > > > > > > > > > > > > > I also found that reverting that hunk results in a 3-4% > > > > > > > improvement in fio > > > > > > > IOPS rates, as well as improvement in average and maximum > > > > > > > latency > > > > > > > as reported > > > > > > > by fio. > > > > > > > > > > > > > > > > > > > Hmm… Provided the sequence numbers still lie within the > > > > > > window, > > > > > > then why would the order matter? > > > > > > > > > > The misordering is so bad that one request is delayed long > > > > > enough > > > > > to > > > > > fall outside the window. The new “need re-encode” logic does > > > > > not > > > > > trigger. > > > > > > > > > > > > > That's weird. I can't see anything wrong with need re-encode at > > > > this > > > > point. > > > > > > I don't think there is anything wrong with it, it looks like it's > > > not called in this case. > > > > So you are saying that the call to rpcauth_xmit_need_reencode() is > > triggering the EBADMSG, but that this fails to cause a re-encode of > > the > > message? > > No, I think what's going on is that the need_reencode happens when > the > RPC is enqueued, and is successful. > > But xprt_request_enqueue_transmit places the RPC somewhere in the > middle > of xmit_queue. xmit_queue is long enough that more than 128 requests > are > before the enqueued request. The test for rpcauth_xmit_need_reencode() happens when we call xprt_request_transmit() to actually put the RPC call on the wire. The enqueue order should not be able to defeat that test. Hmm... Is it perhaps the test for req->rq_bytes_sent that is failing because this is a retransmission after a disconnect/reconnect that didn't trigger a re-encode? > > > > Do the window sizes agree on the client and the server? > > > > > > Yes, both are 128. I also tried with 64 on the client side and > > > 128 > > > on the server side. That reduces the frequency of disconnects, > > > but > > > does not eliminate them. > > > > > > I'm not clear what problem the logic in > > > xprt_request_enqueue_transmit > > > is trying to address. It seems to me that the initial, simple > > > implementation of this function is entirely adequate..? > > > > I agree that the fair queueing code could result in a reordering > > that > > could screw up the RPCSEC_GSS sequencing. However, we do expect the > > need reencode stuff to catch that. -- Trond Myklebust Linux NFS client maintainer, Hammerspace trond.myklebust@xxxxxxxxxxxxxxx
